When non-equilibrium, low-temperature plasmas and catalysts interact, they can exhibit synergistic behavior that enhances the chemical activity above what is possible with either process alone. Unlike thermal catalysis, in plasma-assisted catalysis the non-equilibrium state of the plasma produces reactive intermediates, such as excited species, that may play an important role in the catalytic process. There are two primary plasma-surface mechanisms that could produce this synergy: the effect of the plasma on the catalyst (e.g. enhanced adsorption/reaction of plasma-activated species, change of surface structure/ morphology, hot spots, etc) and the effect of the catalyst on the plasma state. This work focuses on the latter. We use a laboratory-scale, packed bed, dielectric barrier discharge (DBD) reactor to observe the influence of multiple alumina (Al 2 O 3 ) supported, transition metal ammonia (NH 3 ) synthesis catalysts on the plasma electrical and optical properties. We find that while the rates of ammonia synthesis over the materials considered, including
Atmospheric
pressure nonthermal plasmas hold great promise for
applications in environmental control, energy conversion, and material
processing. Even at room temperature, nonthermal plasmas produce energetic
and reactive species that can initiate surface modifications at a
plasma–surface interface, including thin-film nanoparticle
assemblies, in a nondestructive and effective way. Here, we present
the plasma-activated sintering of aerosol jet printed silver thin
films on substrates ranging from glass to delicate materials including
blotting paper, fruits, and flexible plastic. We characterize the
microstructural evolutions and electrical properties of printed films
along with the electrical, thermal, and optical properties of an argon
plasma jet. We demonstrate an electrical conductivity as high as 1.4
× 106 S/m for printed films sintered under atmospheric
conditions in which the surface temperature stays below 50 °C.
These results highlight a future direction where additive manufacturing
of electronic devices can be achieved on flexible and low-melting-point
materials under ambient conditions without requiring additional thermal
processing by utilizing nonthermal plasmas.
Understanding plasma–surface interactions is important in a variety of emerging research areas, including sustainable energy, environmental remediation, medicine, and high-value manufacturing. Plasma-based technologies in these applications utilize surface chemistry driven by species created in the plasma or at a plasma–surface interface. Here, we develop a helical dielectric barrier discharge (DBD) configuration to produce a small-scale plasma that can be implemented in a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) cell and integrated with a commercial Fourier transform infrared (FTIR) spectrometer instrument to study plasma interactions with inert or catalytic solid media. The design utilizes the entire surface of a cylinder as its dielectric, enhancing the plasma contact area with a packed bed. In this study, we characterize the electrical and visual properties of the helical DBD design in an empty reaction cell and with added potassium bromide (KBr) powder packing material in both air and argon gas environments at ambient conditions. The new surface DBD configuration was integrated into a DRIFTS cell and the time evolution of water desorbing from the KBr packed bed was investigated. Measurements show that this configuration can be operated in filamentary or glow-like mode depending on the gas composition and the water content absorbed on KBr solid media. These results not only set the basis for the study of plasma–surface interactions using a commercial FTIR, but also show that controlling the gas environment and water content in a packed bed might be useful for studying different plasma regimes that are typically not possible at atmospheric pressure.
Atmospheric pressure, ambient temperature plasma jets have become a promising candidate for material processing in parallel with developments in additive manufacturing. Recent work has shown that plasma jets can be used to sinter printed nanoparticles at temperatures much lower than typically required for conventional thermal sintering. Here, we conduct a mechanistic study on plasma jet sintering that correlates specific energy input with the electrical conductivity of printed silver films after sintering. Increasing the specific energy input accelerated the sintering process following an Arrheniuslike exponential trend across a large range of conditions, including both helium and argon plasma jets. Although an exponential relationship is also found with the plasma heated substrate temperature, independent studies indicate that heating is not the primary mechanism. These results suggest there is a general behavior that couples the plasma jet with the surface.
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